Xeroradiography device



Nov. 4,1958 M. D. PHILLIPS 2,859,350

' XERORADIOGRAPHY DEVICE Filed May 20, 1954 FIG .2

//z v /l I v INVENTOR. I n MICHAEL D. PHILLIPS M Y QM F'G 3 ATTORNEY 2,859,350 Patented Nov. 4, 1958 United States Patent Ofifice 2,859,350 XERORADIOGRAPHY DEVICE Michael D. Phillips, Columbus, Ohio, assignor, by mesne assignments, to Haloid Xerox Inc., Rochester, N. Y., a corporation of New York Application May 20, 1954, Serial No. 431,132

5 Claims. (Cl. 25065) This invention relates generally to xeroradiography and, in particular to intensification screens used in connection with the production of radiographs through eleciroradiography.

In silver halide radiography, intensification screens are i generated X-rays move at relatively large angles with respect to the primary beam, and their absorption in the screen improves the definition of the image and increases image contrast. Second, the screens act to absorb p11 gmary X-rays and create secondary X-rays having lower voltages than the primary beam. These secondary,

lower energy X-rays are much more easily absorbed and detected by the film than are the higher voltage X-rays. This generally decreases the exposure time needed and since the screen is close to the film, the definition is not decreased seriously, although the secondaries may move at large angles relative to the primaries. In addition,

' secondaries travelling at very divergent angles may be reabsorbed before escaping from the screen itself. As secondaries are created in proportion to the number of primaries reaching a given area of screen, such secondaries give a true representation of the relative absorption of the primaries in the object being examined. Third, when struck by primary high voltage X-rays, screens emit photoelectrons or beta particles. Such electrons or particles ejected from the screen may be absorbed by the film and render it exposed as would light or X-rays. Electrons like the secondary X-rays are emitted in proportion to the amount of radiation absorbed, causing the electrons to produce a picture of the object being examined.

In the field of electroradiography or xeroradiography, an electrically sensitized plate is used in place of silver halide film. The plate is composed of a conductive backing member supporting a layer of material which is a good electrical insulator in the absence of radiation, but presents a lower electrical resistance in, areas where radiation is absorbed or affects the material due to the action of released carriers. This plate is sensitized by uniformly depositing electrostatic charges on the insulating layer, and an image pattern of electrostatic charges is formed on the surface of this layer when areas of the material are made conductive or present a lower resistance to thefiow of electrostatic charges.

layer and only those areas which become conductive Charges on the surface are held. in position-due to the insulating characteristics of this layer is necessary in order to truly reproduce the image in electrostatic image pattern for subsequent development and utilization.

A charged or sensitized xerographic or xeroradiographic plate is essentially different from a sensitized silver halide emulsion. In the first place, the absorption of energy by a xeroradiographic plate canbe developed or recorded only to the extent that the energy becomeseflective in releasing current carriers. The problem, therefore, is to assure absorption of energy in usable form. On the other hand, carriers or electrical conductivity can be provided in many ways other than by photon energy, and devices or techniques not affecting silver halide emulsions can discharge a sensitized xeroradiographic plate either in part or completely. As a typical example, any attempt to use known'intensifying screens in intimate contact with a sensitized plate, will dissipate the electrical charge on the sensitized surface thereby removing all or part of the plate sensitivity from the plate member preventing usage of the plate to produce radiographs. Intimate contact, however, between the screen and the sensitized surface has been found desirable for greater intensifying action and to increase image resolution and contrast by holding to a minimum the distance electrons and X-rays moving at angles with respect to the primary beam will travel.

It is an object of this invention to provide a new X-ray intensifying screen. i

It is a further object of this invention to disclose methods of using an intensifying screen with xeroradiography.

It is another object of the invention to provide new xeroradiographic methods and apparatus wherein proved results are achieved by means of intensifyingv screens comprising a penetrating radiation stopping-surface coated with a thin insulating layer and adapted to be positioned against the charged surface of a xeroradiographic plate.

It is an additional object of this inventionto provide new xerographic methods and apparatus wherein proved results are achieved by means of intensifying screens comprising a penetrating radiation stoppingsur-p face which is also an insulating material and-.which i'sl adapted to be positioned against the chargedsurface of a xeroradiographic plate. v

Other objects and advantages of this invention will be.

apparent in view of the following description thereof considered in the light of the attached drawings wherein: Figure 1 illustrates one embodiment of an intensification screen as contemplated by this invention;

Figure 2 illustrates the process of making a radiographthrough xeroradiography' using .the improvement of this.

' invention; and,

Figure 3 is another embodiment showing exposure of the plate using the improvements of this invention. 7

Referring more particularly to the drawings,;in Fig.1 is shown one embodiment of intensifying screens generally designated 18 wherein intensifying screen 18 is composed of a support surface on which is coated a layer of lead 25. or other material of high atomic number. 011' the lead coating a thin layerof polystyrene 26 or other in-- sulating material is coated.

In Fig. 2 is shown the steps involved in xeroradiog raphy wherein: stage A indicates the charging procedure resulting in a plate generally. designated 19 which has been made sensitive; stage B the exposure of plate 10 to penetrating radiation a source of which is designated as image produced on the surface of plate 10. A uniform;

electrostatic charge is placed on the surface of plate 10,

composed of conductive backing member 15 and insulat ing layer 16 by creating relative movement between corona discharge electrode 13 and plate 10 'while corona dis-' charge electrode 13 is connected to high voltage source 12 V and conductive backing member 15 is at ground potential. Plate carrying a uniform electrostatic charge is now in a sensitized condition. An electrostatic latent image is created-on thesurface of plate 10 composed; of conductive backing member and insulating layer 16-asshow n at stage B of Fig. 2. An object 17 to be radiographedis placed on an intensifying screen generally designated 18 and the-assembly of object 17 and intensifying screen IS is positioned between a source'of radiation 1 1 and-'a plat'e 10. The 'next step in the xeroradiographic process illustrated at stage C is that of development of the electrostatic latent image created at stage B. The plate 10 composed of conductive'backing member 15 and insulating layer- 16 is placed on development box 20. Developer supply 22 produces a cloud 21 of developer particles in air suspension within development box 20. The developer particles: making up cloud 21 carry electrostatic charges which are Opposite in sign to the electrostatic charges making up the electrostatic latent image on the surface of insulating layer 16. Being opposite in charge the particles are attracted to and deposit on areas of chargeon the surface of layer 16 and thereby through particle deposition develop the electrostatic latent image on plate 10,. This image may be viewed, photographed and the like as it exists on the surface of plate 10 or it may be transferred to another surface using conventional xerographic transfer methods and apparatus and may be therepermanently aflixed or otherwise utilized.

Fig. 3* presents another embodiment of this invention wherein intensifying screen 18 is positioned against insulating layer 16 of plate 10 and object 17 rests on conductive backing member 15 and between plate 10 and source 11 of penetrating radiation. 7

To realizethe benefits in xeroradiography that normally flow from the use of intensifying screens, intensifying Screens have now been formed composed of materials of high atomic number on which a very thin layer of an insulating material is coated. Although it is not intended to in any Way limit this invention, and although it is to beunderstood that any material of high atomic number will be effective to stop penetrating radiation as an inten- "sifying body for this new form of intensifying screen, and

although it is to be understood that any effective electrical insulator which may be coated in a thin layer-may be suitable for this form of intensifying screen, screens which have been made include but are not limited tothe following: lead foilcoated with a vitreousselenium layer, lead foil coated with an acrylic base plastic, lead foil coated with polystyrene and the like. Other high atomic Weight materialssuch as gold, silver, and the like are also efiective, but lead and its compounds are generally preferred for economic .reasons if not for other reasons. Methods for forming these screens include but are in no way limited to vacuum evaporation, chemical reactions, dipping, incorporating in a binder, spraying, painting and the like. ,Generally, theinsulatingmaterial willbe coated on the material of high atomic number in that the material of high atomic number is substantially thicker and presents a more suitable base for coating; however, coating on the insulatoris also possible.

Screens formed according to this invention may. be positionedagainst the charged surface of the xeroradiographic plate by'placing the insulating. surface of the screen against the charged surface of the plate.

Experimentation revealed that a minimum separation between the material of high atomic number and thesensitive surface is imperative if maximum image resolution is to be obtained. While beta particles and other secondary radiation will reach the sensitive surface from an intensifying screen not in contact with it, the particles may travel in paths widely divergent from the paths of the X-rays, and image resolution is reduced severely if space even in the order of hundredths of an inch exists between the screen and the sensitive layer.

4? To obtain positioning of the material of high atomic 'number as close as is possible to the sensitized plate surface, thicknesses of the insulating film of the intensifying screen are held to a minimum with a preferable thickness of less than 10 microns. It is also necessary in coating the insulating material to keep the thickness of the coating uniform throughout so that the intensifying screen will have a uniform intensifying effect on the sensitized layer.

It is noted that the lower limit on thickness of the insulating layer of the intensifying screen is controlled by the ability of this layer to prevent electrical breakdown between the charged surface and the lead or like member. This, of course, is dependent upon the potential placed on the plate surface and other related factors which will be obvious to those familiar with the art.

Although this invention has thus far been described in terms of a conductive material coated with an insulating layer, it is to be understood that it is also intended to include within its scope screens wholly composed of elements or combinations of elements of high atomic number and of sufliciently insulating characteristics as, for example, the insulating organic or inorganic salts of silver, gold, lead, bismuth, cobalt, and other similar high atomic numberelements and the like. When necessary a suitable support basesuch as paper, lead foil, or the like, as is shown in Figure 1, may be used with these materials. Another form of screen and the method of making it intended to be encompassed within this invention is a material of high atomic number with an insulating coating on its surface. A typical example is, the oxidation of metals, such as chemically acting on a sheet of lead or lead foil to form on its surface an insulating coating of lead oxide.

The over-all thickness of intensifying screens according to this invention is limited by the effects that .screens produce on impinging penetrating radiation. The locally generated X-rays and beta particles created when radiation strikes the screen often move at large angles in respect to the primary beam and if allowed to travel a considerable distance, image contrast and definition will substantially decrease. On the other hand, the thicker the screen, upto a maximum limit which is dependent on many factors such as, for example, the penetrating power of the beam, the particular high atomic number material and the like, the greater its intensifying effect. The pref erable thickness therefore stated in general terms is as thick a screen as is possible'up to the point beyond which image contrast and resolution would fall below the level desired, or beyond which increases in speed in the sensitive layer disappear. Morespecifically preferred thicknesses range from 0.020 to 0.0005 of an inch.

0 Example I A sheet of lead foil 0.005 was coated with a thin uniform layer of polystyrene by'dipping the lead into a polystyrene lacquerand withdrawing it at a constant rate of speed. The lacquer consisted of about 600 milliliters'of 62% xylene, 30% The polystyrene is designated as polystyrene beads, 5110 color, and 7-Fines formula.

The lacquer was placed in a steel tank. Before coating the lead was cleaned by scrubbing with a cotton pad saturated in acetone followed by an acetone rinse. The lead used was quite bright before this cleaning which obviously did not remove heavy corrosion.

Operating at room temperature the lead was lowered into the lacquer and withdrawn at the rate of 7 inches per minute by a simple Windlass driven .by a synchronous motor. The coating was allowed to dry for 30 minutes in air. A dry coating .of'about 2.5 microns thick was produced in thisway and .the coated foil was testedaand found satisfactory according to this invention.

acetone, and 8% polystyrene.

Example 11 Another method for forming an intensifying screen according to this invention comprises positioning a sheet of lead or a piece of lead foil in an evaporator and evaporating a pure grade of selenium onto its surface from a crucible heated above 300 degrees C. The temperature of the lead material should be controlled and held somewhere below 150 degrees F. Evaporation should be allowed to take place for more than 20 minutes. The thickness of the selenium coating deposit on the lead is controlled by the amount of time the selenium is allowed to deposit and the rate of evaporation of the selenium from the crucible which is controlled by the temperature the crucible is heated to.

An intensifying screen was made in this manner by placing a sheet of lead 0.005 inch thick in an evaporator and placing a charge of selenium in an adjacent molybdenum evaporation boat. The chamber was evacuated to a pressure of about /5 micron of mercury and the selenium was heated. The lead surface was maintained at a temperature below about 100 degrees C. A layer of selenium about microns thick was deposited on the lead. The resulting coating on the lead was placed in surface contact with a xeroradiographic plate during exposure to X-rays to yield greater contrast sensitivity in the finished xeroradiographic print.

Example III A layer of lead resinate may be placed on the surface of a sheet of aluminum foil by heating the lead resinate to a temperature of about 160 degrees C. and dipping the foil into the molten mass. Uniformity of the coating can be achieved by withdrawing the foil at a substantially constant speed. A mass of lead resinate may be prepared by mixing 16% by weight of lead with wood rosin according to the method shown in Industrial and Engineering Chemistry vol. 36, p. 752. A sheet of aluminum foil may be coated by dipping in the molten resinate at 160 degrees C. to form a coating about 0.005 inch thick. The resulting sheet is useful as a xeror-adiographic intensifying screen.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An intensifying screen for xeroradiography to be placed with a first surface in intimate physical contact with the charged surface of a photoconductive insulating layer during exposure of the photoconductive insulating layer to an X-ray image pattern, comprising a unitary solid structural member having an insulating surfacelayer at said first surface thereof and at least including a layer of high atomic number material spaced no more than 10 microns from said first surface of the intensify ing screen. I

2. An intensifying screen in accordance with claim 1 in which said surface layer and said layer of high atomic number comprise lead resinate.

3. An intensifying screen in accordance with claim 1 in which said surface layer consists of polystyrene.

4. An intensifying screen in accordance with claim 1 in which said surface layer consists of vitreous selemum.

5. An intensifying screen in accordance with claim it i3 which said layer of high atomic number consists of References Cited in the file of this patent UNITED STATES PATENTS 2,124,752 Schimkus July 26, 1938 2,666,144 Schaffert et a1 Jan. 12, 1954 2,698,991 Mesick Jan. 11, 1955 OTHER REFERENCES McMaster: New Developments in Xeroradiography, Non-Destructive Testing, pp. 8-25, Summer No. 1951, vol. 10 #1.

The Iron Age, Nov. 29, 1951, pp. 86-89. 

1. AN INTENSIFYING SCREEN FOR XERORADIOGRAPHY TO BE PLACED WITH A FIRST SURFACE IN INTIMATE PHYSICAL CONTACT WITH THE CHARGED SURFACE OF A PHOTOCONDUCTIVE INSULATING LAYER DURING EXPOSURE OF THE PHOTOCONDUCTIVE INSULATING LAYER TO AN X-RAY IMAGE PATTERN, COMPRISING A UNITARY SOLID STRUCTURAL MEMBER HAVING AN INSULATING SURFACELAYER AT SAID FIRST SURFACE THEREOF AND AT LEAST INCLUDING A LAYER OF HIGH ATOMIC NUMBER MATERIAL SPACED NO MORE THAN 10 MICRONS FROM SAID FIRST SURFACE OF THE INTENSIFYING SCREEN. 